4,4'-[1,5-Pentanediylbis(oxy)]bisbenzenecarboximidamide, generically known as pentamidine, is known to be an effective anti-protozoal and fungicidal agent, particularly it has been used in the treatment of trypanosomiasis (sleeping sickness). More recently, since the advent of the AIDS epidemic (Acquired Immune Deficiency Syndrome) pentamidine has been used in the treatment of pneumocystis carinii pneumonia which is often contracted by AIDS and ARC (AIDS Related Complex) patients. Additionally, pentamidine is used in the treatment and prophylaxis of leishmaniasis.
Initially pentamidine was administered either intravenously or by intramuscular injection. More recently investigators have found that an aqueous solution of pentamidine administered by inhalation is useful for the prophylactic or remedial treatment of pneumocystis carinii pneumonia. (U.S. Pat. No. 4,853,416 issued Aug. 1 , 1989).
The present invention results in a new form of administration of pentamidine and its pharmaceutically acceptable salts, by formulating it into a transdermal pharmaceutical composition or a pharmaceutical composition comprised within a transdermal patch together with a penetration enhancer to achieve blood levels of pentamidine which are effective in the treatment and prophylaxis of protozoal and fungal diseases such as pneumocystis carinii pneumonia.
Transdermal delivery of pentamidine offers advantages over the other methods of delivery of pentamidine. An advantage is the ease of application and removal of a transdermal formulation over the 'complex, device assisted aerosol delivery and over the intravenous or intramuscular delivery. This convenience of use offers the benefit of a lifestyle uninterrupted by hospital visits, which are needed when administering pentamidine by other known methods. Administration by IV or intramuscular delivery has certain disadvantages of inadvertent needle sticks that are especially undesirable when working with AIDS or ARC patients. Needle sticks have also been associated with the risk of secondary systemic infections. Transdermal delivery does provide the ability to deliver drugs directly to general circulation. Transdermal delivery of pentamidine is also advantageous in that it can be used in pediatric age groups, whereas aerosol administration of pentamidine cannot be used. Transdermal delivery of pentamidine also avoids the disadvantage of having chronic exposure of health care workers to pentamidine which is a risk associated with aerosol delivery.
Recognizing that the outer layer of the skin, the epidermis, protects the area under the skin from penetration of foreign chemicals, various enhancing agents have been used to deliver drugs transdermally. Substances that help promote drug diffusion through the stratum corneum and epidermis are referred to as skin-penetration enhancers, accelerants, adjuvants and sorption promoters. B. Idson, Cosmetics & Toiletries, 95, 59 (1980) states that the factors affecting drug penetration and consequently, in most cases, effectiveness, are complex. The vehicle that provides ideal conditions for one drug may prove unsatisfactory for another.
Various penetration enhancers are known to be useful in transdermal drug delivery. U.S. Pat. No. 4,863,970, U.S. Pat. No. 4,722,941, U.S. Pat. No. 4,931,283 and EP 351,897 disclose some representative penetration enhancers used in transdermal compositions and for topical administration.